Artificial teeth



y 22, 1962 s. MYERSON ETAL 3,035,347

ARTIFICIAL TEETH Filed Feb. '7, 1957 2 Sheets-Sheet 1 INVENTORS SIMONMYERSON BY VlCTOR H. SEARS w, my; 554/210? ATTORN EYS May 22 1962 FiledFeb. 7, 1957 5. MYERSON ETAL ARTIFICIAL TEETH 2 SheetsSheet 2 INVENTORSSIMON MYERSON VICTOR H. SEARS 057%, fiov zomg 5m AT TO RN EYS Unitedrates Patent poration, Cambridge, Mass., a corporation of MassachusettsFiled Feb. 7, 1957, Ser. No. 638,809 8 Claims. (Cl. 32-2) The presentinvention relates to artificial dental restoratrons, especiallyartificial teeth and artificial dentures and bridgework containing thesame.

Many dentists prefer artificial dentures having plastic teeth becausethey are believed to reduce shock and trauma on the supporting tissuesand they are more perfectly and comfortably adjusted to the patientsarticulation during wear. They are also easier to adapt by thetechniclans in numerous cases. However, plastic posterior teeth,especially of the type having modified occlusal forms, suffer loss ofefiiciency and functional structure by wear. By modified occlusal formswe refer to those forms which depart from the cusp formation of naturalteeth, as for example, the tooth described in U.S. Myerson Patent1,879,419. For convenience, we shall hereinafter refer to such type ofteeth as functional posteriors." Moreover, many patients find it morediflicult to chew certain types of food with plastic than with porcelainteeth.

One of the objects of this invention is to combine the advantages ofhard, dense, Wear resistant, ceramic teeth with those of plastic teethin upper and lower dentures, while at the same time reducing thedisadvantageous effects of each by providing one of the pair of upperand lower dentures with porcelain posterior teeth having a particularnovel and improved occlusal surface construction and the other of suchpair of upper and lower dentures with plastic posterior teeth, alsohaving such particular, novel and improved occlusal surfaceconstruction. Another object is to provide a novel and improved occlusalsurface construction for artifical teeth, especially posterior teeth,which reduces loss by wear by a substantially greater amount than otherocclusal surface constructions, as for example that dmcribed in PatentNo. 1,879,419, when porcelain teeth of one of a pair of dentures areopposed to plastic teeth of the other. Although the occlusal structureof the posterior teeth of this invention has special benefits for use inupper and lower posteriors in which one set of posterior teeth areporcelain and the opposite are plastic, it has many advantages when usedin the conventional manner, i.e. porcelain articulated with porcelain orplastic articulated with plastic. One of the objectionable featuresinherent in artificial denturesis a tendency toward tilting on one sidewhile chewing on the other side, e.g. the right side of the lowerdenture rises when stress is applied to the left, or the upper rightside comes down. Dentures also have a tendency under certaincircumstances to slide forward and backward on their support-s. It is anobject of this invention to stabilize dentures against these dislocatingforces. It is another object of the present invention to providefunctional posterior teeth, which are economical to produce, which areeasy to handle by the dental technician and which by their novel andimproved occlusal surface structure will direct the forces ofmastication so as to stabilize the artificial dentures against tiltingand sliding and protect the cutting area from wear and breakage andwhich have the above mentioned further advantages when teeth of onedenture are porcelain and those of the opposing denture are plastic. Yetanother object is to provide an artificial tooth having an improvedocclusal surface construction. Other and further objccts'and advantagesof the invention will be pointed out hereinafter in the following andmore detailed description and by reference to the accompanying drawingsin which:

FIG. 1 is a front view of a pair of upper and lower dentures embodyingthe present invention and mounted in what is termed centric relation oncasts corresponding in shape to a human mandible and maxilla.

FIG. 2 is a side view of the dentures of FIG. 1;

FIG. 3 is a view in perspective of a lower first molar of the lowerdenture of FIGS. 1 and 2 showing the occlusal construction of thepresent invention applied to a molar;

FIG. 4 is a perspective view of the lower first molar of FIG. 3 taken ata dilferent angle;

FIG. 5 is a view in perspective of a lower second bicuspid of the lowerdenture of FIGS. 1 and 2 showing the occlusal construction of thepresent invention applied to a bicuspid;

FIG. 6 is a view in perspective of the upper denture of FIGS. 1 and 2showing the occlusal construction of the present invention applied tofour upper posterior teeth on each side of the upper denture;

FIG. 7 is a lateral section taken along the line 77 of FIGS. 1 and 2.

All the upper teeth are porcelain and all the lower teeth are plastic.This order may be reversed. Moreover, the anterior teeth of both upperand lower dentures may be made of plastic or porcelain withoutmaterially afiecting the efiiciency or the durability of the denture;

The teeth herein described and illustrated have many advantages overteeth presently available whether they are all made of porcelain or allmade of plastic and whether the opposing teeth are of like or difierentmaterials. However, if plastic teeth are opposed to porcelain teeth, asillustrated in FIGS. 1 to 7, the most important advantages of porcelainas well as those of plastic will be preserved and the disadvantages ofeach are reduced.

In the combination shown in FIGS. 1 to 7 in which plastic is opposed toporcelain loss by wear is so far reduced as to be negligible, in fact,probably beneficial. Loss by wear was determined by two means. First thedentures were processed in the usual manner and closely adapted toarticulation in the patients month by spot grinding the high spots. Asnearly as possible all grinding was done on the plastic teeth. Any areasground on the porcelain teeth were carefully repolished. After one weekof wear final adjustment was made orally and casts of the dentures werethen made from time to time. By this means, a check on the clinical wearwas made. The second method was by use of a machine which rubbedopposing teeth against each other in a mild abrasive mix under carefullycontrolled conditions. This machine has been in use for a period ofyears to determine wear of plastic teeth and has been found thoroughlyreliable. When plastic teeth of the type described in U.S. Patent No.1,879,419 were rubbed against each other the wear loss was considerablygreater than when one of the teeth was porcelain and the other plastic.When plastic and porcelain teeth having the occlusal construction of thepresent invention were rubbed against each other in the same test, thewear loss was markedly less than that of the plastic and porcelain teethhaving the construction of Patent No. 1,879,419.

With reference to the figures, 1 is a porcelain upper first molar, 2 isa porcelain upper second molar, 3 is a porcelain upper second bicuspidand 4 is a porcelain upper first bicuspid, all of which are mounted inthe upper denture base member 5 which is in turn mounted on the upper ormaxillary cast 6. correspondingly, 7 is a plastic lower first molar, 8is a plastic lower second molar, 9 is a plastic lower second bicuspidand 10 is a plastic lower first bicuspid all of which are mounted in alower denture base member 12 which is in turn mounted on the lower cast14. 15 represents the distal side of each tooth (see FIGS. 2 to 19 isthe mesial side, 21 the buccal side and 23 the lingual side. Theocclusal surface of each of the teeth is characterized by a narrowbuccal cutting margin 16 of a buccal cutter 17 (see FIGS. 3 to 7), abroad, flat, lingual crushing area 18, two transverse wedge-shapedcutters 20 in the case of the molars and a single transversewedge-shaped cutter 20 in the case of the bicuspids connecting thebuccal cutting margin 16 and the flat lingual crushing area 18 andclearance channels 22 for the escape of the masticated food from thedepressed areas 24 formed by the sloped side walls of the cutters andcrushing area. The buccal cutting margin 16, the cutting margins 26 ofthe transverse wedge-shaped cutters 20 and the fiat crushing area 18 arepreferably all in one occlusal plane so as to assure unhindered motionwhen in articulation with the oppo site teeth. The mesial buccal marginsof the first upper bicuspid 4 and the mesial and distal margins of thefirst lower bicuspid may be slightly beveled without interfering withfree motion of the mandible since the mandible normally does not retrudein mastication. Moreover, when the dentures are finished and the planeof occlusion established the molars and bicuspids may be altered to givethem a cusp-like appearance. In some cases this may be advisable inorder to further decrease the stress of closing the dentures throughfood. However, it appears best to make this modification when indicatedand after the dentures are processed. The transverse cutters 20preferably extend from the buccal cutter margin 16 in a distal andlingual direction to the crushing area 18 in one set, e.g. the lowerteeth, and in a mesial lingual direction in the opposite set, e.g. theupper teeth.

FIG. 6 shows a set of four upper posterior teeth with a line 29 runningfrom the distal of the second molar to the mesial of the first bicuspidsubstantially mid-way between the buccal and lingual margins of theteeth. We will call the line 29 the occlusal median axis. By referringto this line, it will be seen that the buccal cutting margins 16 and themajor portion of the transverse cutting margins 26 are buccal to thismedian occlusal axis and that the crushing areas 18 are lingual to andpreferably do not cross this axis. The axis usually lies in the samevertical plane as the highest portion or apex of the mandibular ridge34, if the teeth are set up as usually recommended in relation to theridge and as illustrated in FIGURES 6 and 7. The apex of the ridge onone side is designated as 30 and on the other side as 30a. The maxillaryridge is designated as 36, its apex on one side is designated as 32 andthe other as 32a. Consequently, the lingual crushing area 18 willusually be located lingually of 30 and 30a and lingually of 32 and 32a.The forces exerted on the occlusal surface of the teeth duringmastication are imparted to the maxilla and mandible through theseridges, the apical areas of which may be considered as support fulcrumsfor the dentures. What we have termed apical areas are often referred toas the crest or center of the ridge. Preferably, the lingual flatcrushing area 18 of each tooth reaches substantially to the occlusalmedian axis so that it occupies substantially the entire lingual half ofthe occlusal surface of the tooth. It is preferably three times or morebroader than the cutting margin 16 and the cutting margin 26 especiallyin the first molar and second bicuspid teeth. The area thereof ispreferably more than twice the sum of the areas of the cutter margins 16and 26 of each tooth. However, so long as the crushing area 18 of thetooth is substantially larger than the sum of the cutting margin areas26 and 16 thereof and is substantially broader than the cutter margin 16and the cutting margin 26 the advantages of the present invention areobtained. In effect, the areas of the cutting margins 16 and 26 of eachtooth together with the crushing area 18 comprise the masticating areaof the occlusal surface of the tooth and the crushing area 18 is thelargest and .4 broadest portion of the masticating area. Since the flatlingual crushing areas 18 are substantially larger and broader than thecutting margin areas it requires greater pressure to force them throughthe food than do the cutters. Consequently, if the teeth are correctlypositioned by the technician the greatest forces during mastication willbe applied to the dentures and thence to the supporting fulcrums 30,30a, 32 and 32a at and by means of the crushing areas 18 directly overor lingual of the apical areas of the ridges as shown at 42 in FIG. 7.The dentures are thereby stabilized against tilting on the supportfulcrums just as any load applied to a board 44 (FIG. 7) between twosupport fulcrum points 30 and 30a of the board as at 42 will not tiltthe board and any load applied to the board outside these points as at40 will tend to do so. So long as a relatively large, broad crushingarea is provided in the occlusal plane lingual of the vertical extensionof the fulcrum portions 30, 30a, 32 and 32a of the dental ridges, ascompared to the mastieating areas in the occlusal plane buccal of suchfulcrum portions, the forces of mastication will tend to stabilize thedentures.

The stress during mastication is also centralized from the front to backin the first molar and second bicuspid area by making the flat crushingarea 18 of each of these teeth 1 and 3 larger, preferably 50% or morelarger, than the fiat area of each first bicuspid and second molar asillustrated in FIG. 6. This causes the greatest force during masticationto be exerted in these areas of 1 and 3 which are central with respectto the front and back of the dentures whereby front to back sliding ofthe dentures is inhibited.

Preferably the surface of the procelain teeth should be smooth andcapable of being repolished to a high degree of smoothness aftergrinding thereof. Porcelain teeth made in accordance with the methoddescribed in U.S. Patent No. 2,724,166 are satisfactory. The plasticteeth preferably comprise cross linked copolymers, known in the art tobe resistant to solvents and useful for making plastic teeth. One suchcopolymer is a cross linked copolymer of methyl methacrylate.

Although we have described our tooth and its use in relation todentures, it may also be used in other dental restorations, e.g. inbridgework. It is possible to vary the structures described andillustrated without departing from the spirit of this invention. Theterm occlusal median axis as used herein refers to a mesial distal linepassing approximately through the middle of the occlusal surface(approximately midway between the buccal and lingual edges of suchsurface) as illustrated in FIG. 6 by the line 29.

The imaginary line which lies on the occlusal surface of each of thefour posterior teeth illustrated in FIG. 6 will lie approximately in thesame vertical plane as the apex, or crest, of the ridges, as they areoften termed, if the teeth are set up as usually advocated, over thecenter or crest of the ridge and as illustrated in FIG. 6 wherein theteeth have been set up in soft wax on a denture base plate in thepreparation of a trial denture and as illustrated in the finished upperand lower dentures in FIG. 7. It is often necessary to depart from theideal positioning of the teeth in relation to the dental ridges; even inthese cases, the stability of the dentures will be improved by the useof the teeth of this invention wherein the largest and broadest portionof the masticating area of the tooth is located along the occlusallingual margin of the tooth.

While setting up posterior teeth usually includes two molars and twobicuspids on each side there are numerous occasions when one or moreteeth are eliminated.

In the claims which follow, the contacting occlusal surfaces whichcomprise the crushing areas and the cutting areas of the tooth will bereferred to as the masticating areas.

We claim:

1. An artificial tooth having a fiat crushing area and a cutting area onits occlusal aspect, the said crushing area being of generally segmentalshape substantially broader than the cutting area and being locatedalong the lingual occlusal margin of the tooth, said crushing area beingmainly lingual of the median occlusal axis of the tooth and said cuttingarea mainly buccal of said axis, said cutting and crushing areas lyingsubstantially in the same plane.

2. An artificial tooth according to claim 1 wherein said crushing areacomprises approximately 50% of the occlusal surface of the tooth.

3. An artificial tooth having a crushing area and cutting area on itsocclusal aspect, the said crushing area being substantially broader thanthe cutting area and being located along the lingual occlusal margin ofthe tooth, said cutting area comprising a buccal cutting margin and atransverse cutter extending between the buccal cutting margin and thesaid crushing area.

4. An artificial tooth having a crushing area and cutting area on itsocclusal aspect, the said crushing area being substantially broader thanthe cutting area and being located along the lingual occlusal margin ofthe tooth, said cutting area comprising a buccal cutting margin and atransverse cutter extending between the buccal cutting margin and thesaid crushing area, and a groove to clear the masticated food from theocclusal face of the tooth, said cutting area lying substantially in aplane extending substantially from the mesial to the distal side of thetooth.

5. An artificial tooth having a crushing area and cutting area on itsocclusal aspect, the said crushing area being substantially broader thanthe cutting area and being located along the lingual occlusal margin ofthe tooth, said cutting area comprising a buccal cutting margin and atransverse cutter margin extending between the buccal cutting margin andthe said crushing area, said buccal cutting margin, transverse cuttingmargin and crushing area lying in substantially the same plane.

6. In a combination in an upper and lower denture, an upper posteriortooth and an opposing lower posterior tooth, each of which has amasticating area comprising a crushing area and a cutting area on itsocclusal aspect, the crushing area comprising the broadest portion ofthe masticating area and being located along the lingual occlusal marginof the tooth, one of said posterior teeth being of smooth denseporcelain and the other of a plastic material.

7. An artificial tooth having a fiat crushing area and a cutting area onits occlusal aspect, said crushing area being of generally segmentalshape substantially broader and larger than the cutting area and beinglocated along the lingual occlusal margin of the tooth, said cuttingarea comprising the buccal cutting margin of said tooth and beingsubstantially flat in a mesial-distal direction and lying insubstantially the same plane as said crushing area.

8. An artificial tooth having a substantially flat crushing area and acutting area on its occlusal aspect, the said crushing area beingsubstantially broader and larger than the cutting area and being locatedalong the lingual 0cclusal margin of the tooth, said cutting areacomprising a buccal cutting margin, said cutting area beingsubstantially flat in a mesial-dista-l direction and lying substantiallyin the same plane as said crushing area, said flat crushing area beingbroader and larger than said cutting area in the buccal-lingualdirection along at least the major portion of the dimension of theocclusal aspect of the tooth in the mesial-distal direction.

References Cited in the file of this patent OTHER REFERENCES DentalDigest, April 1944, p. 166. Dental Survey, November 1935, pp. 32-36.

